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Comet plunge reveals solar secrets

Paul Sutherland, News Editor
12 June 2013, 12:06

Sen—In December 2011, space telescopes witnessed an event that astonished astronomers. A comet plunged deep through the atmosphere of the Sun and survived.

Comets are reckoned to be pretty insubstantial things, despite their sometimes lengthy, spectacular tails. So this ball of rock and ice, called Comet Lovejoy (C/2011 W3), had been expected to break up and become vaporised in the encounter.

In fact the comet came out relatively unscathed, grew a fresh magnificent tail and became an impressive sight for astronauts on the International Space Station as well as on Earth.

Lovejoy’s close encounter has been extremely useful for solar scientists because it has allowed them to study a region deep within the Sun’s atmosphere, or corona, that is otherwise near impossible to observe.

Comet Lovejoy rounds the Sun

A movie showing Comet Lovejoy's brush with the Sun, hidden behind an occulting disk to mask its brilliance. Credit: NASA/SOHO

Now views in the extreme-ultraviolet region of the spectrum from three solar spaceprobes have provided new information on the characteristics of the magnetic fields embedded in the region through which Comet Lovejoy passed.

Researchers from several different institutions have produced a report for the journal Science this week about their results. A co-author was Dr Karel Schrijver, of the Lockheed Martin Advanced Technology Center (ATC).

Dr Schrijver, principal investigator of the Atmospheric Imaging Assembly on board NASA’s Solar Dynamics Observatory (SDO), said: “The corona shapes most of the space weather storms that impact Earth. The only part of the corona that we can study with observatories is the part we can see.

“Comet Lovejoy flew through the corona down to a height of only 10 per cent of the solar diameter, where there is almost nothing that we can image. It is essentially an ultra high vacuum with a density even lower than where the International Space Station orbits Earth.

“But when Lovejoy flew through, material from its warming surface evaporated, forming a tail that then lit up brightly enough to be observed. “What we hope to learn eventually is how the Sun’s magnetic field is distorted as it becomes part of the solar wind that blows past all the planets, and thereby to better predict when violent solar eruptions threaten Earth’s space environment.”

As well as SDO, telescopes on the twin spacecraft of NASA’s Solar Terrestrial Relations Observatory (STEREO) observed the comet plunge.

Comet Lovejoy, named after the amateur astronomer who discovered it, Terry Lovejoy of Australia, is a member of the Kreutz family of sungrazing comets. They are fragments of a single giant comet that broke apart back in the 12th century. The Solar and Heliospheric Observatory (SOHO) sees small fragments falling into the sun every few days. Lovejoy was a much larger member.

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